Physics 
Q
.
A 8000kg engine pulls a train of 5 wagons, each of 2000kg, along a horizontal track. If the engine exerts a force of 40000N and the track offers a friction force of 5000N, then calculate:
(a) The net accelerating force:
(b) The acceleration of the train; and
(c) The force of wagon 1 on wagon 2.
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Given : Mass of engine M=8000 kg
Mass of each wagon m=2000 kg
Frictional force acting in backward direction f=5000 N
(a) : The net force acting on the train F
′
=F−f=40000−5000=35000 N
(b) : Let the acceleration of the train be a
∴ F
′
=(5m+M)a
35000=(5×2000+8000)a ⟹a=1.944 ms
−2
(c) : External force is applied directly to wagon 1 only. The net force on the last four wagons is equal to the force applied by wagon 2 by wagon 1.
Let the acceleration of the wagons be a
′
35000=(5m)a
′
⟹35000=10000×a
′
Acceleration of the wagons a
′
=3.5 ms
−2
Mass of last 4 wagons m
′
=4×2000 kg
∴ Net force on last 4 wagons F
1
=8000×3.5 =28000 N
Thus force on wagon 2 by wagon 1 is 28000 N.
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